1. Field of the Invention
The present invention relates to an electronic device that has a substrate mounted with an electronic circuit and accommodated in a housing and to a cooling unit for cooling the electronic device.
2. Description of the Related Art
Recently, various types of mobile personal computers (abbreviated as PC hereinafter) have come into widespread use. One such a PC is a so-called notebook PC composed of a main unit incorporating an arithmetic circuit and having a keyboard on the top surface thereof and a display unit having a display screen and being capable of folded onto the main unit. Another type of such a PC is a pure-tablet (slate) PC that incorporates an arithmetic circuit and has a display screen on the top surface thereof, to which a keyboard is optionally externally connected.
Such mobile PCs are made thinner to reduce the overall size and weight while maintaining the required display screen size, whereas the mobile PCs have more capabilities to meet various needs. For this reason, in a typical mobile PC, multiple electronic components are mounted on both surfaces of the substrate fixed in the housing. In addition, for the sake of layout, several heat generating components are often mounted on the substrate. Thus, when heat generating components are mounted on both surfaces of the substrate, heat from the heat generating components should be radiated effectively.
For example, in Japanese Patent Laid-Open No. 2005-223099, there is proposed the cooling system that has a heat conductive cover for covering a heat generating component and a heat radiating fin and a refrigerant channel between the cover and the heat radiating fin. However, the system is too complicated in structure to be applied to heat generating components mounted on both surfaces of the substrate. Moreover, the system may go against the demands for a thinner device and cost reduction.
In Japanese Patent Laid-Open No. 2001-244665, there is proposed the structure in which heat generating components, which are mounted on both surfaces of a substrate, are made to abut the respective heat radiating components. Specifically, the bottom surface of a first heat generating component mounted on a first surface of the substrate abuts a first heat radiating component through an opening formed in the substrate right under the first heat generating component. On the other hand, the top surface of a second heat generating component mounted on a second surface of the substrate abuts a second heat radiating component. Accordingly, heat from both the first and second heat generating components are radiated at the same time.
However, the above structure has a problem in terms of electrical connection, as the substrate has an opening formed through the first and second surfaces in the area where the first heat generating component is mounted. Therefore, such a structure cannot be applied to, for example, a BGA (ball grid array) package in which the bottom surface of a heat generating component serves for a solder joint. Rather it seems easy and preferable in terms of layout for RGB package or the like to mount the first heat generating component not on the first surface but on the second surface of the substrate without forming an opening in the substrate.